Environmentally benign rare earth pigments: effect of calcium dopant and tuning of bandgaps for different color hues

Purpose As there is a strong inducement to develop new colored inorganic materials to substitute the current industrial pigments that are based on toxic metals hazardous to health and the environment, the purpose of this paper is to invent environmentally benign rare earth-based colorants as viable alternatives to the traditional toxic pigment formulations. Herein, the authors developed a series of rare earth pigments having the general formula Ca0.1 Ln0.9 PO4 ( Ln = Y , Pr , mixed rare earth oxides, RE and Di). After studying all the optical properties, the authors have gone for some coloring application in plastic like PMMA. Design/methodology/approach The designed pigments were synthesized by traditional solid-state method. Stoichiometric amounts of each reagent were mixed in an agate mortar and the mixtures were calcined at optimized temperature 1000 °C for 4 h in electric furnace followed by auto–cooling. The samples were characterized by X-ray diffraction diffraction, UV–vis spectroscopy, scanning electron microscope (SEM), particle size distribution, color coordinates determination, acid/alkali test, thermo gravimetric (TG) analysis and CIE–1976 L*a*b* color scales. Among the various lanthanide ions and calcium ion as dopant, the pigment composition shows various hues ranges from green to yellow. The designed pigments consist of non–toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates like PMMA. Findings The present investigations establish that various color hues can be achieved by the incorporation of suitable chromophore metal ions like calcium in various rare earth host lattice by tuning of the band gaps. The coloring mechanism is based on the strong absorption of the pigments in the blue and red regions due to electronic transitions of the micro states of rare earth ion. The pigment composition shows various hues ranges from green to yellow. The coloring mechanism is based on the tuning of band gap by the dopant like calcium in various rare earth host lattice. In addition, this pigment was chemically and thermally stable. Finally, it has applied in plastics like PMMA. Research limitations/implications Mechanism of the color appearance using band calculations and on possible applications of rare earth phosphate powders as pigments in plastics and paints have not been explored much. However, the properties of the Ca-doped rare earth phosphate implies that this material has a potential to be applied as a satisfactory pigment for coating or coloring except for glaze, which may cause a side reaction at high temperatures, especially taking into consideration the economics and ecologies. The possibility of Ca2+ incorporation in CePO4 with monazite structure-type has been established. Practical implications The designed pigments consist of non-toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates. Thus, the present environmental friendly pigment powders may find potential alternative to the classical toxic inorganic pigments for various applications. Social implications There is a strong incentive to design new colorants based on inorganic materials to substitute for industrial pigments that are based on heavy elements hazardous to health and the environment. However, several industrial yellow pigments such as cadmium yellow (CdS), chrome yellow (PbCrO4) and nickel titanium yellow (TiO2-NiO-Sb2O3) contain the harmful elements (e.g. Cd, Pb, Cr and Sb) for the human body as well as the environment. The designed pigments consist of non-toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates. Thus, the present environmental friendly pigment powders may find potential alternative to the classical toxic inorganic pigments for various applications. Originality/value There is a strong incentive to design new colorants based on inorganic materials to substitute for industrial pigments that are based on heavy elements hazardous to health and the environment. However, several industrial yellow pigments such as cadmium yellow (CdS), chrome yellow (PbCrO4) and nickel titanium yellow (TiO2-NiO-Sb2O3) contain the harmful elements (e.g. Cd, Pb, Cr and Sb) for the human body as well as the environment. So, the authors have developed new class of inorganic pigments that are both non-toxic and environmentally unimpeachable, while preserving or even exceeding the optical, thermal and chemical characteristics of the existing commercial pigments. The developed colorants find practical applications in polymer matrix like PMMA.

PERFORMANCE TEST AND HEAT RESISTANCE OF PHYSICAL AND CHEMICAL COATED IRON OXIDE BLACK PIGMENT

The current development strategy of inorganic pigments is to develop technologies, such as high coloring ability, low oil absorption, easy dispersion, heat resistance, and nontoxicity. As the largest colored inorganic pigments, iron oxide pigments are widely used in building materials, coatings, rubber, plastics, paint, etc. In this paper, black iron oxide pigment was used as the carrier, and alumina substance was used as the support. Precipitation method was used to synthesize the aluminum oxide-coated iron oxide black composite pigment under different experimental conditions, and the coated iron was studied by XRD, SEM and TEM characterization methods. The structure of the black pigment, discuss the influence of the coating temperature, reaction pH, coating method, neutralizing acid and other factors on the microstructure of the composite material and the performance of the pigment. The experimental results show that, through co-current coating, the temperature of the reaction system of 80∘C and the reaction pH of 10–11 are the best parameters for coating. The oil absorption, tinting power, hiding power and dispersion power of the coated iron black were tested, and the performance of the iron black pigment was greatly improved after the coating. The heat resistance and light fastness of iron black were tested through the color difference change experiment. The experimental results showed that the heat resistance and light fastness of iron black pigment showed good performance after coating.

Pigmenty a barevnost tradičních venkovských staveb na jižní Moravě

The article describes an interdisciplinary study that uses the means of ethnology and materials science. This approach is quite unusual in the Czech environment. Specifically, it concerns detailed materials analyses of samples of plaster which were acquired during ethnological research on selected recent buildings in South Moravia. The studied plaster samples from folk buildings in the Znojmo area are probably from the twentieth century. However, it cannot be ruled out that the buildings are older. In addition to traditional and mostly inorganic pigments, the plaster samples were also coloured using synthetic pigments, which corresponded to their availability on the market. Besides the description of the set of samples, the article also demonstrates the potential of applying natural-scientific methods to analyse plaster and its pigments for ethnology. At present, these methods are common in materials engineering and are used in restoration work.

White pigments

White pigments are inorganic pigments, whose optical action is mainly based on non-selective light scattering. White pigments do not show absorption in the range of visible light, but have high scattering power leading to high hiding power in their applications. The greater the difference between the refractive index of the white pigment and that of the surrounding medium, the higher the scattering power.